Introduction to Explosive Welding

Amit Joshi

(B.E Mechanical, A.M.I.Prod.E)

Dept. of Metallurgical Engineering & Material Science,

Indian Institute of Technology - Bomby.

Introduction

Explosive welding
is a solid state welding process, which uses a controlled explosive detonation
to force two metals together at high pressure. The resultant composite system
is joined with a durable, metallurgical bond.

Explosive welding under high velocity
impact was probably first recognized by Garl in 1944. Explosive welding was
first recognized as a possibility in 1957 in the United
States when it was observed by Philipchuck
that metal sheets being explosively formed occasionally stuck to the metal
dies. Between that and now the process has been developed fully with large
applications in the manufacturing industry.

It has been found to be possible
to weld together combinations of metals, which are impossible, by other means.

The Process

This is a solid state joining process.
When an explosive is detonated on the surface of a metal, a high pressure
pulse is generated. This pulse propels the metal at a very high rate of speed.
If this piece of metal collides at an angle with another piece of metal, welding
may occur. For welding to occur, a jetting action is required at the collision
interface. This jet is the product of the surfaces of the two pieces of metals
colliding. This cleans the metals and allows to pure metallic surfaces to
join under extremely high pressure. The metals do
not commingle, they are atomically bonded. Due to this fact, any metal may
be welded to any metal (i.e.- copper to steel; titanium
to stainless). Typical impact pressures are millions of psi. Fig. 1 shows the explosive welding process.

Explosives

The commonly used high explosives
are –

Explosive

Detonation velocity ,
m/s

RDX (Cyclotrimethylene
trinitramine, C3H6N6O6

8100

PETN (Pentaerythritol
tetranitrate, C5H8N12O4)

8190

TNT (Trinitrotoluene,
C7H5N3O6)

6600

Tetryl (Trinitrophenylmethylinitramine,
C7H5O8N5)

7800

Lead azide (N6Pb)

5010

Detasheet

7020

Ammonium nitrate
(NH4NO3)

2655

Applications

1) Joining of pipes and tubes.

2) Major areas of the use of this method are heat exchanger tube
sheets and pressure vessels.